Technology for low-cost electronically steered phased arrays
This dissertation presents a low-cost packaging technology and CMOS transceiver IC for electronically steered phased array transmit/receive (T/R) modules. T/R modules are a critical element for phased-array antennas, and the module cost-performance trade greatly affects the entire phased-array antenna architecture.
A highly integrated X-band active antenna module is implemented based on a novel System-in-Package technique. The proposed multi-layer packaging scheme utilizes low-cost laminates and embeds the radiating element as an integral part of the package. The package architecture facilitates the integration of transceiver block with antenna in a single compact unit. The ability of the packaging technique to be implemented using standardized automated processes and materials ensures that the technique can be successfully implemented for commercial applications.
The packaging scheme has been characterized by implementing single-polarization and dual polarization active SiP module. The single polarization module contains commercially available GaAs T/R switches, an LNA, a PA and mixer. Polarization switches are added to the transceiver path for dual-polarization module. Measurements demonstrated that package resonances are effectively suppressed. The packaging does not affect the embedded planar antenna and transceiver MMIC's performance. The active antenna module is compact (15x15x1.5mm3) with an antenna gain of 6.5dB and antenna efficiency better than 80% that is comparable to the performance of currently available high-cost SiP solutions. Measured element patterns for dual-polarization module were well behaved with cross-polarization levels down roughly 18dB.
A linear 1x4 sub-array is implemented based on the characterized active antenna module. This small array allowed investigation of some of the issues facing arrays of BGA active antenna modules, namely fitting the elements together and coupling to feed lines. No feed line disruptions were observed. Scan impedance variation is another concern for array based environment. Simulations of infinite array of SiP modules indicate that proposed technique barely affects the scan impedance performance of the planar active antenna as compared to a standard patch antenna.
To increase the cost-effectiveness of proposed module, CMOS technology is of interest due to 4x reduction in cost as compared to GaAs technology. A CMOS IC (0.18μm technology) that combines a power amplifier and low noise amplifier has been designed, fabricated and measured. The antenna switch is eliminated by incorporating DC bias switching. An on-chip balun is implemented to overcome the power limitations of CMOS technology (due to low breakdown voltage and lossy substrate). The LNA-PA combination has a P1dB of 14.2dBm (transmit) and noise figure (receive) of 6.5 dB in X-band. This is comparable to the stand-alone X-band CMOS LNA, PA and T/R switch performance reported till date.
For CMOS power amplifier applications, distributed effects in wide devices lead to saturation of output power with the increase in device width, thus further limiting the power performance for CMOS technology. These distributed effects have been analyzed and a closed form analytical solution for the phenomenon is presented.